Conformational dependence of long-range spin-spin coupling constants in 2,6-dichlorobenzylfluoride

1969 ◽  
Vol 47 (19) ◽  
pp. 3688-3690 ◽  
Author(s):  
T. Schaefer ◽  
C. M. Wong ◽  
K. C. Tam
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Double Resonance ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Double resonance experiments on the proton magnetic resonance spectrum of 2,6-dichlorobenzylfluoride yield the signs of the long-range coupling constants between the ring protons and the fluorine nuclei and protons in the fluoromethyl group. The signs and magnitudes of the long-range couplings are discussed in terms of their dependence on the conformation of the fluoromethyl group.

Long-range proton–19F spin–spin coupling interactions in phenyltrifluorosilane

1977 ◽  
Vol 55 (18) ◽  
pp. 3243-3247 ◽  
Author(s):  
William J. E. Parr ◽  
T. Schaefer ◽  
K. Marat
Keyword(s):  
Long Range ◽  
Resonance Spectrum ◽  
Base Point ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hindered Rotation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

Analysis of the proton magnetic resonance spectrum of phenyltrifluorosilane yields the spin–spin coupling constants between the fluorine nuclei and the protons. These are compared with the analogous long-range coupling constants in benzotrifluoride, toluene, and phenylsilane and are rationalized in terms of coupling mechanisms. The coupling over six bonds is assessed as a base point for the estimation of hindered rotation about the carbon–silicon bond.

A proton magnetic resonance determination of the small rotational barriers about the C—Si bond in phenyl derivatives of chloro and methyl silanes

1977 ◽  
Vol 55 (3) ◽  
pp. 557-561 ◽  
Author(s):  
William J. E. Parr ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Low Energy Conformations

The long-range spin–spin coupling constants between protons bonded to silicon and ring protons in C6H5SiH3, C6H5SiH2Cl, C6H5SiH2CH3, C6H5SiHCl2, and C6H5SiH(CH3)2 are determined from the proton magnetic resonance spectra of benzene solutions. A hindered rotor treatment of the barrier to internal rotation about the C—Si bond, in conjunction with the coupling constants over six bonds, allows the deduction of the low-energy conformations for C6H5SiH(CH3)2 and for C6H5SiHCl2, as well as of barriers of 1.0 ± 0.2 kcal/mol. The approach becomes less reliable for C6H5SiH2CH3 and for C6H5SiH2Cl and, particularly for the latter compound, the derived barrier is very likely an upper limit only. Ab initio molecular orbital calculations of the conformational energies are reported for C6H5SiH3, C6H5SiH2Cl, and for C6H5SiHCl2.

scholarly journals Proton Magnetic Resonance Spectrum of 1-Penten-3-yne. INDO and CNDO/2 Molecular Orbital Calculations on Long-Range Spin–Spin Coupling Constants in Enynes

1972 ◽  
Vol 50 (12) ◽  
pp. 1863-1867 ◽  
Author(s):  
L. Ernst ◽  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Benzene Solution ◽  
Parent Compound ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The high resolution p.m.r. spectra of 1-penten-3-yne in carbon disulfide and in benzene solution are analyzed. Long-range spin–spin coupling constants are discussed in terms of σ and π electron contributions. Comparisons are made with the isomeric 2-methyl-1-buten-3-yne and the parent compound, vinylacetylene. The results of INDO and CNDO/2 molecular orbital calculations are compared to the experimental coupling constants. It is concluded that the π electron contribution to 5J in enyne systems is +0.6 to 0.7 Hz and that σ electron contributions are rather small, the transoid ("pseudo-zig–zag") being larger than the cisoid one. Observed allylic coupling constants in the propene derivative are compared with the calculated values, including those for propene and 2-cyanopropene, available in the literature.

scholarly journals Proton Magnetic Resonance Spectrum of 2-Chloroaniline-15N. Long-range Coupling Constants to Amino Protons from all Ring Protons

1971 ◽  
Vol 49 (22) ◽  
pp. 3627-3635 ◽  
Author(s):  
R. Wasylishen ◽  
T. Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum ◽  
Proton Exchange ◽  
Coupling Constants ◽  
Amino Group ◽  
Fast Rotation ◽  
The One

The p.m.r. spectra of 2-chloroaniline and 2-chloroaniline-15N in benzene and toluene solutions are analyzed at 60 and 100 MHz under conditions where the amino protons are exchanging intermolecularly and also where they are not exchanging. The spectrum of 2-chloroaniline-H15ND in the absence of amino proton exchange is observed between −48 and 80 °C. In all situations fast rotation about the C—N bond evidently occurs. Long-range couplings of the amino protons to all ring protons are observed and their signs are determined. The nonplanarity of the amino group is discussed in terms of the long-range couplings, of the one-bond 15N–H couplings, and of the two-bond H–H couplings in the amino group. The signs and magnitudes of the coupling constants between the ring protons and 15N are also determined.

Through-space or proximate 19F,19F and 19F,1H spin–spin coupling constants in some benzenesulfonyl fluoride derivatives

1976 ◽  
Vol 54 (22) ◽  
pp. 3564-3568 ◽  
Author(s):  
William J. E. Parr ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Conformational Preference ◽  
Fluorine Nucleus ◽  
Spin Coupling Constants ◽  
The Difference ◽  
Spin Spin Coupling

The analysis of the fluorine and proton magnetic resonance spectra of 2,4,6-trimethylbenzenesulfonyl fluoride and of 2,5-difluorobenzenesulfonyl fluoride yields the signs and magnitudes of the spin–spin coupling constants containing a through-space component. The coupling between the fluorine nucleus and the methyl protons over five bonds is +1.9 Hz, opposite in sign to the −3.1 Hz observed for the corresponding coupling in 2,6-dimethylbenzoyl fluoride. The difference of 5 Hz is possibly a consequence of the different conformational preference of the SO2F and COF substituents. The coupling over four bonds between the fluorine nucleus on the side chain and that on the ring is +11.6 Hz in 2,5-difluorobenzenesulfonyl fluoride. It is argued that this value indicates a preference of the S—F bond for a plane lying, on average, nearly perpendicular to the benzene ring. Similar indications are noted for pentafluorobenzenesulfonyl fluoride and for pentafluorobenzenesulfinyl fluoride.

1H nuclear magnetic resonance and molecular orbital studies of 2-formylstyrene. Three significant nonplanar conformers at 300 K

1995 ◽  
Vol 73 (12) ◽  
pp. 2208-2216 ◽  
Author(s):  
Ted Schaefer ◽  
Scott Kroeker ◽  
David M. McKinnon
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Formyl Group ◽  
Trans Conformer ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The 1H nuclear magnetic resonance spectra of 2-formylstyrene, from dilute solutions in CS2–C6DI2 and acetone-d6, are analyzed to yield precise chemical shifts and spin–spin coupling constants. The long-range coupling constants imply a conformational distribution in which the O-trans conformer is 55% abundant in both polar and nonpolar environments. They also imply that the vinyl group, on average, is twisted out of the aromatic plane to a much larger extent than in styrene. The 6-31G* basis set gives an ab initio potential for the torsion of the vinyl moiety with a relatively deep minimum at 38° out-of-plane, for the O-cis conformer. For the O-trans conformer, two minima are found, one at 45° and another at 129.6°. Essentially the same potential is obtained with the 6-31G** basis. The latter corresponds to a close approach of the hydrogen atom of the formyl group and π orbitals or the β-carbon atom of the olefinic side chain. This local minimum is interesting in terms of a hypothesis used to explain the photochemistry of the molecule. The long-range coupling constants are consistent with the conformational properties calculated for the free molecule; they also indicate no significant difference between the conformational behaviour of the molecule in the two solvents. A proximate coupling constant of −0.16 Hz exists between the formyl and methine (α) protons. The latter is strongly deshielded in the presence of the formyl group, so that it becomes even less shielded than some of the aromatic protons. Keywords: 1H NMR, 2-formylstyrene (o-vinylbenzaldehyde); long-range spin–spin coupling constants, 2-formylstyrene; conformations, three nonplanar of 2-formylstyrene; molecular orbital calculations, conformations of 2-formylstyrene.

Unusual Long-Range Spin–Spin Coupling in Norbornane-2,3-diones. Proton Magnetic Resonance Spectrum and X-Ray Structure Analysis of 6-endo-Bromo-1,5,5-trimethylnorbornane-2,3-dione

1973 ◽  
Vol 51 (24) ◽  
pp. 4076-4079 ◽  
Author(s):  
G. F. Hambly ◽  
Jeanette Leitch ◽  
Peter Yates ◽  
S. C. Nyburg
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Structure Analysis ◽  
Mirror Symmetry ◽  
Proton Magnetic Resonance ◽  
Substituent Effects ◽  
Proton Magnetic Resonance Spectrum ◽  
Spin Coupling ◽  
X Ray ◽  
Spin Spin Coupling

Several norbornane-2,3-diones show in their proton magnetic resonance spectra an unusual long-range spin–spin coupling, 4J46λ = 1.0–1.5 Hz. An X-ray structure analysis of 6-endo-bromo-1,5,5-trimethylnorbornane-2,3-dione shows that the norbornane framework deviates only slightly from mirror symmetry. This makes it unlikely that the unusual coupling in the norbornane-2,3-diones is due to distortion of the norbornane framework and lends credence to the view that it is due to substituent effects.

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